This invention relates to a method of cooling beer in a fermentation tank having a large volume.
Techniques for effecting the main fermentation and the secondary fermentation (lagering) of beer by the use of separate cylindrical tanks or one cylindrical tank, of large capacity, installed out-of-doors, have recently been developed. Examples thereof are disclosed in U.S. Pat. Nos. 3,374,726 and 3,433,148. The term "fermentation tank" referred to in the present description is a general term for identifying tanks devised to effect the main fermentation and the secondary fermentation (lagering) successively within one tank and tanks devised to effect the main fermentation and the secondary fermentation (lagering) in separate tanks. The term "a tank of a large capacity" herein means a tank having a volumetric capacity of more than 200 Kl, generally 500 to 600 Kl, and a height of 10 m or more, and such large capacity tanks are to be distinguished from conventional fermentation tanks or lagering tanks which have a capacity of from 10 Kl to scores of Kl and a height of generally no more than about 3 m. The present invention relates to an improved method of cooling beer within a large volumetric capacity fermentation tank such as defined above.
During the main fermentation of beer, in the initial and middle stages thereof wherein fermentation is effected while maintaining the liquid temperature at 8.degree. to 10.degree. C., the liquid is intensely agitated by heat convection and the carbon dioxide gas bubbles generated by the fermentation and, therefore, the cooling of the liquid is performed efficiently. But, in the final stage of the fermentation, and particularly in the case where the same fermentation tank is used for lagering the beer, it is necessary for the beer to be cooled down to about 0.degree. C., and it is also necessary in the course of lagering for aging the beer to maintain the beer at a temperature of 5.degree. C. to -1.degree. C. (the freezing temperature of beer is about -2.degree. C.). Further, because beer is about 92 to 93 wt. % water, the properties of water, particularly the density of water being highest at about 4.degree. C., are important factors. Therefore, in the case of the conventional method of cooling beer in a cylindrical fermentation tank having a volumetric capacity as large as 500 Kl, e.g., a method of cooling beer by introducing a coolant into a coolant coil inside the tank, because no convection of beer occurs and the cooling relies on heat transfer alone, without agitation, there occurs the physical phenomenon that the temperature of the beer in the lower part of the fermentation tank stays at about 4.degree. C. or thereabout and it does not appreciably change. Moreover, if the beer is cooled down to below 4.degree. C., there occurs the peculiar phenomenon that the cooled portion of the beer rises in the tank.